The invention applies to the field of antenna arrays. For many applications, directive radiation is desired. As an illustration, detection and communication with a target require radiation to be focused in a preferential direction. Avoiding electromagnetic pollution outside useful areas is another example of an application involving relatively directive radiation.
In order to increase the directivity of an antenna array, the use of reflectors such as parabolic antennas, the arraying of antennas and the association of coupled antennas like for antennas of the Yagi-Uda type are known from the state of the art.
However, these solutions strongly increase the size of the antenna array. Indeed, the directivity of a reflective antenna is estimated conventionally by the formula
  D  =                    4        ⁢        π                    λ        2              ⁢    A  wherein A is the visible projected surface along the main radiation direction. Notably, this means that for a reflecting disc of radius R,
  D  =                    4        ⁢                  π          2                ⁢                  R          2                            λ        2              .  
It is also known how to jointly energize a radiation mode of the transverse electric (TE) type and a magnetic mode (TM) within a same antenna array. An antenna array structure supporting such an operation is called a Huygens source. For example, in document FR-A-2 949 611, a structure is proposed, based on a resonator consisting of a ring-shaped conducting helix producing a Huygens source with a reduced antenna size.
However, the maximum directivity level which may be attained with this type of antenna array structure is limited by the directivity of the ideal Huygens source, which is of 4.7 dBi. The unit dBi means “decibel relative to an isotropic source”. Generally, the directivity of an antenna is normally expressed in dBi, by taking as a reference an isotropic antenna, i.e. a fictitious antenna of the same total radiated power which uniformly radiates in all the directions with radiation of 0 dBi.